Koji Nishio began his football career as a defender for Nankatsu SC, the city selection elementary school team, wearing jersey number 3. His performance during the team selection test caught the eye of coach Tadashi Shiroyama, securing him a regular defender position. An injury sustained during the national championship forced him out of the tournament, with Ryo Ishizaki taking his place. For junior high, Nishio joined Otomo Middle School alongside teammate Hanji Urabe, rather than attending Nankatsu Middle School. At Otomo, he underwent rigorous training with Urabe, Takeshi Kishida, and Masao Nakayama to challenge Tsubasa Ozora's team, forming the "Otomo Quartet." Despite their development and strong efforts, Otomo lost the Shizuoka regional final to Nankatsu. Following this defeat, Nishio supported Nankatsu during their national tournament campaign. Nishio was not selected for the Japanese national youth teams during middle school or his early career. His involvement with a J-League club remains unspecified. However, he later reappeared in the *Rising Sun* arc, joining the Japanese national team as an emergency replacement for injured players during the match against Germany. Physically, Nishio measured 142 cm and 35 kg in elementary school, growing to 164 cm and 52 kg by middle school. His sole noted technique is the cooperative "Otomo Quartet" tactic, emphasizing teamwork with his Otomo peers. In non-manga adaptations, the Tecmo game series presented a different account: depicting Nishio as a player from Nishigaoka Elementary School (contradicting the manga) and later as part of Seinan Miracle in *Captain Tsubasa IV*. He also participated in a training camp in *Captain Tsubasa V* but was not selected for subsequent matches. Additionally, Nishio is alternatively known as "Franky Gilbert" in some European dubs and "Jorge" in Latin American adaptations. Concrete information about his activities beyond the *Rising Sun* arc or potential retirement is unavailable.